Conventional spin torque transfer (STT) magnetic random access memory (MRAM) stores a charge state, representative of a binary bit, by passing a charge current through a magneto tunnel junction (MTJ), which has a tunnel barrier stacked between a free magnetic layer and a pinned (or fixed) magnetic layer. The charge current affects the magnetic moment of the free layer to either be aligned or anti-aligned with the magnetic moment of the pinned layer (which is unaffected by the current). As the alignment of magnetic moments remains unchanged in the absence of the charge current, the MTJ stack behaves as a bi-stable system suitable for memory storage.
However, STT MRAM has a number of disadvantages that have stood in the way of widespread adoption of this technology for memory storage: (1) STT MRAM exhibits slow write speeds (e.g., 10's of ns) as compared to existing static RAM (SRAM) and dynamic RAM (DRAM) technology with write speeds on the order of 100's of ps and a few ns, respectively; (2) large write currents are required as compared to existing technologies; (3) large write currents passing through the MTJ breakdown the oxide and limit endurance; (4) if read current is sufficiently large, it can undesirably flip the MRAM cell; and (5) die density is limited by the need for at least one access transistor per bitcell.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.